The KOSPI traded at 6,944.14, up 1.9 percent, after pushing back above the 7,000 line early in the session and then slipping under it.
The index added 130.80 points.
Foreigners bought a net 572.8 billion won ($404.3 million) of Seoul shares, while individuals sold a net 321.0 billion won ($226.6 million) and institutions a net 233.4 billion won ($164.7 million).
SK hynix traded at 1,682,000 won ($1,187), up 5.6 percent.
Samsung Electronics rose 0.9 percent to 270,500 won ($191), a fraction of the move in its smaller rival, leaving the gap between the two memory makers as wide as it has been during this rally.
The trigger was SanDisk's investor day in the United States, where the company set a target of roughly 80 percent non-GAAP gross margins from fiscal 2028 through fiscal 2030 and disclosed supply agreements with eight customers covering about two-thirds of bit shipments by fiscal 2028. SanDisk shares closed up about 13.7 percent Thursday, and SK hynix's U.S.-listed shares rose about 7 percent alongside them.
Traders in Seoul read the NAND flash targets as a signal that pricing power in memory is holding rather than peaking, which lands more directly on SK hynix than on the more diversified Samsung Electronics.
Softer U.S. inflation data gave the rally a second leg. Consumer prices rose 0.1 percent in July and producer prices were flat, readings that trimmed market odds of a Federal Reserve rate increase at the September meeting and sent the S&P 500 to a record.
The bid broadened past chips. Hyundai Motor climbed 6.8 percent to 447,000 won ($315) and Kia rose 3.1 percent to 141,700 won ($100), while SK square gained 3.2 percent to 1,153,000 won ($814).
Not everything joined. Hanwha Aerospace fell 4.2 percent to 1,135,000 won ($801), the sharpest decline among the largest listings.
The KOSDAQ, the secondary market for smaller and technology companies, edged up 0.2 percent to 863.03, well behind the main index in Seoul.
In Tokyo, the Nikkei 225 traded at 69,374.53, up 1.6 percent.
The won traded at 1,416.80 per dollar, marginally stronger than Thursday.
Copyright ⓒ Aju Press All rights reserved.